Users must drive an IP2Bus_Data to ZERO when Bus2IP_CS is not asserted; otherwise, the prior IP2Bus_Data value will be OR'd with the content of the registers they are intending to read. This will cause an incorrect data read.
A note has been added to the signal table for plb_ipif_v1_00_f, plb_ipif_v2_01_a, and plb_ipif_v2_02_a.
This has been fixed in the latest EDK 8.1i Service Pack, available at:
The first service pack containing the fix is EDK 8.1i Service Pack 1.